This invention relates to an apparatus for the sterilizing of flexibly packaged food items in a continuous process in which microwaves are used to heat the items to sterilizing temperatures.
Food, which is to be sterilized in an apparatus in accordance with the invention, preferably is hermetically sealed in pouches or similar containers made of non-metallic materials which are transparent or permeable to microwaves and which will effectively exclude infiltration of microorganisms into the food over a time period of several years. Such packaging materials are available in today's commercial market in numerous forms of polymeric films, including laminates of two or more such films. For example, polyethylene, polypropylene, polyethylene terephthalate, and numerous other polymeric films are available for such purposes and do a good job of protecting food packaged therein against recontamination after it has been sterilized in a sealed package.
Sterilization of packaged foods in containers which are transparent to microwaves is well-known in the art as illustrated by U.S. Pat. No. 3,718,082, which relates to continuous microwave heating of sealed or unsealed packages of food being conveyed through a microwave apparatus on a single conveyor belt. However, this system has the disadvantage that the heat generated within the packaged food is lost from the food at a rapid rate, thus requiring the input of much more microwave energy to increase the temperature of the food to a sterilizing level and to maintain it at such a level than would be required if means were provided for preventing loss of the thermal energy from the food until sterilization is complete.
It is, therefore, an object of the invention to provide apparatus for thermally processing a food hermetically sealed in a plurality of flexible packages intended for long-term storage of the food, the thermal processing to be accomplished by microwave irradiation of the plurality of flexible packages continuously and by maintaining in the food substantially all of the heat generated therein by the microwaves until the food has become sterilized, and thereafter cooling the packages of sterilized food to a temperature low enough to prevent bursting of the packages prior to discharge of the packages of sterilized food from the apparatus into the external atmosphere.
Another object of the invention is to provide apparatus for sterilizing food in sealed flexible pouches continuously with microwaves in a shorter time than has heretofore been possible for a given input of microwave energy.
A further object of the invention is to provide apparatus for sterilizing food in sealed flexible pouches continuously with microwaves at a substantially reduced processing cost.
Other objects and advantages will be apparent from the following description of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims.